This guide explains how to use the 2-channel independent ground method provided by the VMI3 to simultaneously measure the waveforms of four injectors using only two physical channels, and how to compare and analyze the injection time and voltage status of each cylinder.
Guide Video (English)
Step 1: Probe Connection for 4-Channel Simultaneous Measurement
The VMI3 allows the (+) and (-) terminals of a single channel to be used as independent measurement sources. Using this, connect to all four injector control lines.
- Test Vehicle: Seltos (SP2) G2.0 MPI
- Injector Control Line Connections:
- CH.A (+) Probe: Connect to injector 1 control line (A1 waveform on screen)
- CH.A (-) Probe: Connect to injector 3 control line (A2 waveform on screen)
- CH.B (+) Probe: Connect to injector 4 control line (B1 waveform on screen)
- CH.B (-) Probe: Connect to injector 2 control line (B2 waveform on screen)
- Common Ground: Connect the oscilloscope’s black common ground clip to the battery (-) terminal.
Step 2: Oscilloscope Screen and Trigger Settings
- Measurement Range: Voltage 80V / Time 1.0 ms (to observe injector operating voltage and injection time)
- Peak Mode: To avoid missing the high surge voltage that occurs momentarily when injector operation is cut off, turn on
[Peak Mode]. - Keep the engine idling.
Step 3: Injection Time and Voltage Analysis
Intuitively compare the characteristics of the four injector waveforms aligned on the screen.
- Injection Time: Compare the length of the section where the waveform drops and stays near 0V to check whether the amount of fuel injected into each cylinder is consistent.
- Counter Electromotive Force (CEMF Surge): Check if the peak voltage (e.g., around 50–60V) generated when the coil magnetic field collapses appears evenly across all injectors. If the peak voltage is too low, suspect possible damage inside the injector coil.
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